Semiconductor ignition system



March 1, 1966 e. o. HUNTZ INGER ETAL 3,238,415

SEMICONDUCTOR IGNITION SYSTEM Filed Dec. 6, 1962 2 Sheets-Sheet 1 QINVENTORS GERALD o. HUNTZINGER WILLIAM 0. women.

BY ARM THEIR ATTORNEY March 1, 1966 s. o. HUNTZINGER ETAL 3,238,416

SEMICONDUCTOR IGNITION SYSTEM 2 Sheets-Sheet 2 Filed Dec. 6, 1962INVENTORS THEIR ATTORNEY GERALD o. HUNTZINGER BY WILLIAM D. woBRELLUnited States Patent 3,238,416 SEMICONDUCTOR IGNITION SYSTEM Gerald D.Huntzinger and William D. Worrell, Anderson, 11141., assignors toGeneral Motors Corporation, Detroit, Mich, a corporation of DelawareFiled Dec. 6, 1962, Ser. No. 242,686 14 Claims. (61. 315-195) Thisinvention relates to ignition systems for internal combustion enginesand more particularly to an ignition system wherein a semiconductor suchas a transistor controls the current flow through the primary winding ofthe ignition coil.

One of the objects of this invention is to provide a semiconductorcontrolled ignition system which maintains a substantially constantenergy storage time in the primary winding of the ignition coil over theentire speed range of the engine. With this arrangement, the amount ofpower required to operate the ignition system is reduced to a minimum.

Another object of this invention is to provide an i nition systemwherein a semiconductor switch means such as a transistor controls thecurrent flow through the primary winding of an ignition coil and whereinthe semiconductor switch means is controlled by .a system that includesa magnetic pick-up, the system including means whereby the time that thesemiconductor switch means is turned on is maintained substantiallyconstant both at high and low speeds of the engine.

Still another object of this invention is to provide an ignition systemwherein a semiconductor switch means such as a transistor controls thecurrent flow through the primary winding of an ignition coil and whereinthe conduction of the transistor is controlled by a magnetic pickuphaving a coil winding in which pulses of voltage are induced insynchronism with the engine, the coil Winding being connected with acapacitor which is charged in accordance with the speed of the engineand in accordance with the on time of the semiconductor switch meanswhich controls current flow through the primary winding of the ignitioncoil. In this arrangement, the voltage which is induced in the pick-upcoil must overcome the charge on the capacitor and the on time of thesemiconductor switch means that controls primary winding current istherefore maintained substantially constant over a widely varying speedrange of the engine.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being bad to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE 1 is a schematic circuit diagram of a breakerless transistorignition system made in accordance with this invention.

FIGURE 2 is a schematic circuit diagram of a system which is amodification of the system illustrated in FIG- URE 1.

Referring now to FIGURE 1, the reference numeral designates an enginehaving a plurality of spark plugs each of which is designated byreference numeral 12. The spark plugs 12 are supplied with electricalenergy through a current distributing mechanism which in this case takesthe form of a distributor cap 14 having a plurality of fixed contacts orelectrodes 16. It is seen that the electrodes 16 are connected with thespark plugs 12 by conductors 18. A rotor contact 20 of conventionalconstruction is provided which is connected with a high voltage lead 22.The rotor contact 20 is driven by the engine 10 and swings in closeproximity to the fixed contacts 16 in a manner well-known to thoseskilled in the art.

The high voltage lead 22 which is electrically con- 3,238,416 PatentedMar. 1, 1966 ICC nected with the rotor contact 20 is connected to oneside of a secondary winding 24 of an ignition transformer 26. Theignition transformer 26 has a primary winding 28 one side of which isconnected with a junction 30. It is seen that one side of the secondarywinding 24 is also connected with the junction 30 and that the junction30 is connected with a grounded power supply conductor 32.

The power supply conductor 32 is connected with the negative side of aDC. voltage source designated by reference numeral 34. This DC. voltagesource 34 is shown as a battery and on a motor vehicle electricalsystem, the battery will, of course, be charged by a generator which cansupply the ignition system of this invention when the engine isoperating and the output voltage of the generator is greater thanbattery voltage. The positive side of battery 34 is connected withconductor 36 and this conductor is connected with a conductor 38 througha manually operable ignition switch 40. When the ignition switch 40 isclosed, the power supply conductor 32 is at a negative potential whereasthe conductor 38 is at a positive :potential.

The ignition system of this invention uses .a magnetic pick-updesignated in its entirety by reference numeral 42. This magneticpick-up includes a rotor 44 which is driven by the engine 10 and whichis formed of magnetic material. It is seen that the rotor has eightradially eX- tending teeth which can become progressively aligned withthe pole faces 46a and 46b of a magnetic core 46. A permanent magnet 48is provided for causing a flow of magnetic flux through the magneticcore 46 and through the rotor 44 when a pair of radially extending teethcomplete the magnetic circuit between the pole faces 46a and 46b. Apick-up coil 50 is wound on the magnetic core 46 and an AC. voltage isinduced in this pick-up coil 50 which has a frequency which is afunction of the speed of the engine 10. It will be appreciated that themagnetic flux for the core 46 could be provided by an electrical fieldcoil rather than the permanent magnet 48 if so desired.

It is pointed out that as a pair of teeth are moving into alignment withpole faces 46a and 46b, a voltage of one polarity is induced in the coilwinding 50 and as the radially extending teeth then move out ofalignment with the pole faces 46a and 4612, a voltage of an oppositepolarity is induced in the coil winding 50. Since there are eightradially extending teeth on the rotor 44, there will be eight cycles ofalternating voltage induced in the coil winding 50 during one revolutionof the rotor 44. It will, of course, be appreciated that the number ofteeth for the rotor 44 will correspond to the number of cylinders of theengine 10 and this can be varied to suit the engine.

It is noted that the magnetic pick-up 42 and the current distributingdevice 14 could be made as one unit and could be made in accordance withthe teaching of patent application Serial No. 126, 406, filed on June16, 1961, and assigned to the assignee of this invention.

One side of the pick-up coil 50 is connected with junction 52 whereasthe opposite side of this pick-up coil is connected with junction 54.The junction 52 is connected with the base electrode of a three terminalsemiconductor switch means which in the embodiment of the inventionshown takes the form of a PNP transistor 55. The emitter electrode oftransistor 55 is connected with junction 56 on power conductor 38. Thecollector electrode of transistor 55 is connected to one side of theprimary winding 58 of a coupling transformer 60. The opposite side ofthe primary winding 58 is connected with junction 62 on power conductor32. The coupling transformer has a secondary winding 64 which isconnected respectively with junctions 66 and 68.

The junction 68 is connected with the emitter electrode of another threeterminal semiconductor switch means which takes the form of a PNPtransistor 70. The base electrode of transistor 79 is connected withjunction 66 and thus is connected to one side of the secondary winding64. The collector electrode of transistor 76 is connected to one side ofthe primary winding 28 of the ignition transformer 26. It is seen that aZener diode 72 is connected across the emitter and collector electrodesof transistor 70. The junction 68 is connected to one side of a resistor74 via a conductor 76. A resistor 78 con nects the junction 52 with thejunction 79 on conductor 76.

The junction 66 which is connected with the base electrode of transistor78 is connected to one side of a capacitor 80 via the lead wire 82. Theopposite side of capacitor 80 is connected with junction 84. A diode 86connects the junction 84 with conductor 38 and another diode 88 connectsthe junctions 84 and 54. A capacitor 90 is connected between junction 54and the conductor 38.

When the engine is being cranked or when the engine is operating andwhen the ignition switch 40 is closed, the ignition system is energized.With the engine 10 operating, the rotor 44- rotates and pulses of A.C.voltage are induced in the coil winding 58 with a polarity which causesjunction 54 to be positive with respect to junction 52, the transistor55 is biased to conduct in its emitter-collector circuit. Thus, avoltage of this polarity causes the emitter of transistor 55 to bepositive with respect to the base electrode thereof and therefore beginsto turn on the transistor 55 in its emitter-collector circuit. With thispolarity of voltage, the capacitor 96 is also partially charged by thevoltage induced in the pick-up coil 50.

When transistor 55 turns on in its emitter-collector circuit, currentcan flow from junction 56, through the emitter-collector circuit oftransistor 55, through primary winding 58 and then to junction 62. Thecurrent build up in the primary winding 58 causes a voltage to beinduced therein which is proportional to the rate of buildup of current.This causes a voltage to be induced in the secondary winding 64 which isof such a polarity that junction 68 is driven positive with respect tojunction 66. This applies a forward bias to the transistor 76 whichtends to turn it on in its emitter-collector circuit. As transistor 70turns on, a current also flows from junction 68, through resistor 74,through diode 86, through capacitor 80 and then back to the oppositeside of the secondary winding 64 at junction 66. This causes thecapacitor 80 to be charged with a polarity such that junction 84 ispositive with respect to junction 66. As will become more readilyapparent hereinafter, the charge on capacitor 80 is used to assist inestablishing the on time for the transistors 55 and 70 in the nextcycle.

When transistor 70 turns on in its emitter-collector circuit, currentwill flow through resistor '74, through the emitter-collector circuit oftransistor 70 and through the primary winding 28 of the ignitiontransformer. At low engine speed, the pick-up coil furnishes enoughsignal to the base of transistor to turn it on but not sufficient toproduce saturation and allow full steady state current to pass throughwinding 58. Because of the drop in resistor 74, junction 79 will be morenegative than junction 56 allowing additional base current to flow fromjunction 52 through resistor 78, junction 79, conductor 76,emitter-collector of transistor 70, primary 28 and to battery 34.Transistor 55 is thus kept fully conducting until it receives a turn offsignal from pick-up coil 50.

As the rotor 44 continues to rotate, the voltage induced in coil winding50 eventually reverses its polarity. As this polarity reverses, thejunction 52 is driven positive and the base electrode of transistor 55therefore is driven positive with respect to its emitter. This willcause the transistor 55 eventually to turn off in its emitter-collectorcircuit. As transistor 55 turns off in its emitter-collector circuit,the flow of current through the primary Winding 58 starts to decreaseand a voltage is induced in the secondary winding 64 which causes thebase of transistor 70 to be positive with respect to its emitter. Thisturns off the transistor 7 0 in its emitter-collector circuit and alarge voltage is then induced in the secondary winding 24 of theignition coil 26 when the circuit to the primary winding 28 issubstantially opened by the turn-ing off of transistor 70. The highvoltage which is induced in the secondary winding 24 is applied to oneof the spark plugs 12 through the high voltage conductor 22, the rotorcontact 20, one of the electrodes 16 and one of the conductors 18.

The Zener diode 72 has a Zener voltage which is slightly lower than theemitter to collector break down voltage rating of transistor '70. Withthis arrangement, the Zener diode protects the transistor 70 from thevoltage induced in the primary winding 28 of the ignition trans formerwhen the current flow through the primary winding 28 is interrupted by aturning off of the transistor 70.

The voltage which is induced in the secondary winding 64 of the couplingtransformer to turn off the transistor will cause the potential atjunction 66 to become more positive than the potential at junction 68.This will cause a current to how from junction 66, through lead wire 82,through capacitor 80, through diode 88, through capacitor 90, throughconductor 38, through resistor '74 and then back to the opposite side ofthe secondary winding 64- via conductor '76 and junction 68. This causesthe capacitor to be charged such that the junction 54 is at a morepositive potential than the conductor 38. The amount of charge which isaccumulated by the capacitor is dependent upon the value to which thecapacitor 86 was charged during the time that the transistor 7 0 wasturned on. The amount of charge which was accumulated by the capacitor90 determines the on time of the transistor 55 for a part of theignition cycle. It thus is seen that in order to bias the base electrodeof transistor 55 negative with respect to the emitter, it is necessaryto overcome the potential which has been accumulated by the capacitor90. It thus is seen that transistor 55 will not turn on until thevoltage induced in the pick up coil 56 is built up to a value requiredto overcome the charge on capacitor 98.

This provides a time delay for the turning on of the transistor 55 inits emitter-collector circuit. The time delay in turn on of thetransistor 55 is made to be inversely proportional to engine speed sothat the total on time of transistor 55 is maintained relativelyconstant over the entire engine operating speed range. The charge whichis accumulated on capacitor 90 is dependent upon the sum of the chargessupplied by the pick up coil 50 and the charge supplied by the secondarywinding 64 of the coupling transformer 60 through capacitor 80 whentransistor 70 is turned off. The voltage induced in the pick up coil 50as the rotor 44 rotates is proportional to rotor speed. The rotor 44 isdriven at engine speed or at some multiple of engine speed and thevoltage induced in the pick up coil 50 is therefore proportional toengine speed. The portion of the charge accumulated in capacitor 90which is supplied by the pick up coil 50 is directly dependent on thevoltage induced in the pick up coil 50 while transistor 55 is turned on.Since this voltage increases with engine speed, the portion of thecharge on capacitor 90 which is supplied by the pick-up coil 50 isdirectly dependent upon engine speed. It will be appreciated that theportion of the charge accumulated by capacitor 90 which is supplied bythe secondary winding 64 of the coupling transformer 60 through thecapacitor 80 is proportional to the on time of transistor 55.

In practice, the voltage induced in the pick up coil 50 builds up at aslow rate at low engine speeds and at a fast rate at high engine speeds.It therefore is seen that a given charge on capacitor 90 will cause moretime delay at low engine speeds than at high engine speeds. At

low engine speeds, the on time of transistor 55 tends to be long, butthis increases the charge on capacitor 90 supplied from the secondarywinding 64 of the coupling transformer and therefore causes the on" timeto be shorter. At high speeds, the on time of transistor 55 tends to beshort, and this causes less charge to be supplied from the secondarywinding 64 of the coupling transformer so that less delay and turn on ofthe transistor 55 results. Proper choice of circuit components willcause the on time of transistor 55 at low engine speeds to be onlyslightly longer than at high engine speeds.

With the ignition system of this invention, the transistor 70 is turnedon only during the time that transistor 55 is turned on and this meansthat the current fiowing through the primary winding 28 of the ignitiontransformer will always have built-up to nearly the same value beforetransistor 70 is turned off. This will result in less power dissipationin the circuit at lower engine speeds than would be required if thepercent on time was allowed to remain constant over the entire enginespeed range.

Referring now particularly to FIGURE 2, an ignition system isillustrated which is identical with the system shown in FIGURE 1 withthe exception that a feedback coil 92 is provided which is connectedbetween one side of the primary winding 58 of the coupling transformerand the junction 94 on conductor 32. The system of FIGURE 2 is in otherrespects identical with the system of FIGURE 1 and the same referencenumerals have therefore been used in FIGURE 2 to identify equivalentparts in each of the figures.

The system of FIGURE 2 operates in the same fashion as the system ofFIGURE 1 with the exception of the effect of the feedback coil 92. Thuswhen the transistor 55 is turned on, a current will flow through thefeedback coil 92 as well as through the primary Winding 58 of thecoupling transformer 60. As the current starts to flow in the feedbackcoil 92, a voltage will be induced in this coil which will beproportional to the rate of current build up in this coil. This willcause a voltage to be induced in the pick up coil 50 which will be ofsuch a polarity as toincrease the forward bias on the transistor 55.This will cause more drive current to flow from the pick up coil 50through capacitor 90 and the emitter to base circuit of transistor 55.This increase drive current will cause more current to flow through theemitter to collector junction of transistor 55, the primary 58 of thecoupling transformer 60 and the feedback coil 92. As a result, thetransistor 55 is more readily driven to its fully turned on state.

It can be seen from the foregoing, that the only difference in theoperation of the systems illustrated in FIG- URES 1 and 2 is that inFIGURE 2, the feedback coil 92 operates to more readily turn thetransistor 55 fully on when the voltage induced in the pick-up coil 50is of such a polarity as to switch this transistor on.

It will be appreciated that the transistor ignition systems illustratedin both FIGURES 1 and 2 are arranged such that they require a minimumamount of power to operate them. This is accomplished by providing asystem wherein the transistor 70 which controls primary Winding currentis turned on for substantially the same time during both high speed andlow speed operation of the engine.

The term three terminal semiconductor switch means as used in thespecification and claims is intended to cover transistors and any otherthree terminal semiconductors such as controlled rectifiers which arecapable of being used in place of transistors.

While the embodiments of the present invention as herein disclosed,constitute a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. An ignition system for an internal combustion engine comprising, anignition transformer having a primary winding and a secondary winding, asource of direct current power, magnetic pick-up means including apick-up coil, said magnetic pick-up means having a part which is adaptedto be driven by the engine, a first transistor having emitter, collectorand base electrodes, means connecting the emitter-collector circuit ofsaid first transistor in series with said source of direct current powerand in series with said primary winding of said ignition transformer, asecond transistor having emitter, collector and base electrodes, acoupling transformer having a primary winding and a secondary winding,means connecting said secondary winding of the coupling transformeracross the emitter and base electrodes of said first transistor, meansconnecting the primary winding of said coupling transformer in serieswith the emitter-collector circuit of said second transistor and acrosssaid source of direct current power, means connecting one side of saidpick-up coil with the base electrode of said second transistor, acapacitor connecting the opposite side of said pick-up coil with oneside of said source of direct current power, and circuit means forcharging said capacitor from the secondary winding of said couplingtransformer.

2. An ignition system for an internal combustion engine comprising, asource of direct current power, an ignition energizing circuit, a firsttransistor having emitter, collector and base electrodes, meansconnecting the emitter-collector circuit of said first transistor inseries with said ignition energizing circuit and in series with saidsource of direct current power, a second transistor having emitter,collector and base electrodes, means coupling the collector circuit ofsaid second transistor with the base circuit of said first transistor, avoltage pulse generating means driven by said engine and including acoil winding, means connecting one side of said coil winding with thebase electrode of said second transistor, a first capacitor connectedwith an opposite side of said coil winding, a second capacitor, acharging circuit for said second capacitor connected with the baseelectrode of said first transistor, and a charging circuit for saidfirst capacitor including said second capacitor and connected with thebase electrode of said first transistor.

3. The combination according to claim 2 wherein the means for couplingthe collector circuit of the second transistor with the base circuit ofthe first transistor is a coupling transformer.

4. In combination, an internal combustion engine, at least one sparkplug for said engine, an ignition transformer having a primary windingand a secondary winding, semiconductor switch means, a source of directcurrent power, means connecting the current carrying terminals of saidsemiconductor switch means in series with said primary winding and inseries with said source of direct current power, control means connectedwith said semiconductor switch means for turning said semiconductorswitch means on and off, said control means having a part driven by saidengine, means for developing a first signal that is a function of enginespeed, means for developing a second signal which is a function of theturn-on time of said semiconductor switch means, and means for delayingthe turning on of said semiconductor switch means in response to saidfirst and second signals.

5. The combination acccording to claim 4 wherein the semiconductorswitch means is a transistor.

6. The combination according to claim 4 wherein the control means is amagnetic pick-up having a pick-up coil in which voltages are induced ofan alternating polarity.

7. The combination according to claim 4 wherein the means for delayingthe turning on of the semiconductor switch means includes a capacitor.

8. In combination, an internal combustion engine, at least one sparkplug for said engine, an ignition transformer having a primary windingand a secondary winding, means connecting said secondary winding withsaid spark plug, semiconductor switch means, a source of 1? directcurrent, means connecting the current carrying terminals of saidsemiconductor switch means in series with said primary winding and inseries with said source of direct current, control means connected withsaid semiconductor switch means for turning said semiconductor switchmeans on and olf, said control means having a part driven by saidengine, means for developing a first voltage that is a function ofengine speed, means for developing a second voltage which is a functionof the turn on time of said semiconductor switch means and means fordelaying the turning on of said semiconductor switch means in responseto said first and second voltages.

9. The electrical system according to claim 8 where the means fordelaying the turning on of the semiconductor switch means includes acapacitor which is charged by said first and second voltages.

10. An ignition system for an internal combustion engine comprising, aspark plug for said engine, an ignition transformer having a primarywinding and a secondary winding, means connecting said secondary windingwith said spark plug, a source of direct current power, a semiconductorswitch means connected between said source of direct current power andthe primary winding of said ignition coil, control means driven insynchronism with said engine for causing said semiconductor switch meansto be turned on and off and means for causing the on time of saidsemiconductor switch means to be substantially constant over the varyingspeed range of said engine, said last-named means including means fordelaying the turning on of said semiconductor switch means in accordancewith engine speed, the amount of delay increasing as engine speeddecreases.

11. The combination according to claim 10 wherein the semiconductorswitch means is a transistor.

12. The combination according to claim 10 wherein the control meansincludes a magnetic pick up having an output coil in which pulses ofalternating voltage are induced in synchronism with operation of theengine.

13. An ignition system for an internal combustion engine comprising, aspark plug for said engine, an ignition transformer having a primarywinding and a secondary winding, means connecting said secondary windingwith said spark plug, a source of direct current, a semiconductor switchmeans connected between said source of direct current and said primarywinding 40 of said ignition coil, control means including means drivenin synchronism with said engine for applying Q"! turn-on and turn-offsignals to said semiconductor switch means whereby said semiconductorswitch means is turned on and off in accordance with the signal appliedto it from said control means, said turn-on and turn-oil signals beingdeveloped between predetermined angles of rotation of said engine, andmeans for maintaining the on time of said semiconductor switch meanssubstantially constant over the varying speed range of the engine, saidlast-named means including means for delaying the turning on of saidsemiconductor switch means as engine speed decreases, said delay beingincreased as engine speed decreases.

14. An ignition system for an internal combustion engine comprising, aspark plug for said engine,.an ignition coil having a primary windingand a secondary winding, means connecting said secondary winding withsaid spark plug, a source of direct current, a semiconductor switchmeans connected between said source of direct current and said primarywinding, a voltage pulse generating means driven. in synchronism withsaid engine and operative to supply time spaced turn-on and turn-offpulses for controlling the conduction of said semiconductor switchmeans, the spacing between said turn-on and turn-off pulses being afunction of the speed of rotation of said engine, and a control meanscoupling said pulse generating means to said semiconductor switch meansfor applying said turn-on and turn-off pulses to said semiconductorswitch means, said control means including means for delaying theturning on of said semiconductor switch means when one of said turn-onpulses is developed, said delay being increased as engine speeddecreases whereby a substantially constant. on time is maintained forsaid semiconductor switch means over the varying speed range of saidengine.

References Cited by the Examiner UNITED STATES PATENTS 2,941,119 6/1960Ford 3l5206 X 3,060,350 10/1962 Rywak 30788.5 3,087,090 4/1963 Konopa 3l5--2'O9 3,131,327 4/1964 Quinn 315-223 X 3,145,324 8/1964' Race 315-207GEORGE N. WESTBY, Primary Examiner.

DAVID J. GALVIN, Examiner.

D. E. SRAGOW, Assistant Examiner.

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, ANIGNITION TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING, ASOURCE OF A DIRECT CURRENT POWER, MAGNETIC PICK-UP MEANS INCLUDING APICK-UP COIL SAID MAGNETIC PICK-UP MEANS HAVING A PART WHICH IS ADAPTEDTO BE DRIVEN BY THE ENGINE, A FIRST TRANSISTOR HAVING EMITTER, COLLECTORAND BASE ELECTRODES, MEANS CONNECING THE EMITTER-COLLECTOR CIRCUIT OFSAID FIRST TRANSISTOR IN SERIES WITH SAID SOURCE OF DIRECT CURRENT POWERAND IN SERIES WITH SAID PRIMARY WINDING OF SAID IGNITION TRANSFORMER, ASECOND TRANSISTOR HAVING EMITTER, COLLECTOR AND BASE ELECTRODE, ACOUPLING TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING,MEANS CONNECTING SAID SECONDARY WINDING OF THE COUPLING TRANSFORMERACROSS THE EMITTER AND BASE ELECTRODES OF SAID FIRST TRANSISTOR, MEANSCONNECTING THE PRIMARY WINDING OF SAID COUPLING TRANS-